CD26 (DIPEPTIDYL-PEPTIDASE-IV DPP-IV) AS A NOVEL MOLECULAR MARKER FORDIFFERENTIATED THYROID-CARCINOMA

In this report we show that CD26 (dipeptidyl peptidase IV/DPP IV) is a novel molecular marker for differentiated thyroid carcinoma. Northern -blot analysis of 22 various thyroid tissues revealed that CD26 is a m ore specific marker of differentiated thyroid carcinoma than 3 proto-o ncogenes previously reported to increase mRNA expression in thyroid ca rcinomas: c-met, c-erbB-2 and EGF-R. A comparative study of 3 CD26 ass ays, Northern blotting, immunohistochemical staining and activity stai ning clearly showed that CD26 enzyme activity staining is the most spe cific assay for differentiated thyroid carcinoma, yet the easiest to p erform. Activity staining of 216 thyroid tissues detected CD26 in all 52 papillary carcinomas and all 5 follicular carcinomas, while all 58 cases of Graves' disease were CD26-negative. Among benign neoplasms, 5 4 of 55 adenomatous goiters and 29 of 33 follicular adenomas were CD26 -negative. Staining intensity of the enzyme activity was relative to t he degree of CD26 mRNA expression. Southern-blot study showed no gene amplification or major translocation of the CD26 gene in 7 papillary c arcinomas examined. Based on this study, ectopic expression of CD26 in differentiated thyroid carcinomas is thought to be mainly caused by i ncreased CD26 mRNA expression. In conclusion, CD26 activity staining i s a simple, specific assay which should be added to the usual patholog ical examinations in order to distinguish differentiated thyroid carci nomas from benign thyroid diseases. (C) 1995 Wiley-Liss, Inc.